Assignment 6: Implementing myprintf()

In this assignment, you will write a modified version of the printf() function in SPARC assembly code which can be called from a C program.

The ANSI C prototype for the myprintf() function is as follows:

    void myprintf(const char *format, ...);

The format contains two kinds of items: plain characters and conversion specifications. Plain characters are simply copied to the standard output. Conversion specifications begin with a % and end with a conversion operation character from the set: u, s, and %.

%u interprets the next argument in the parameter list as a 32-bit unsigned integer and prints its decimal representation.

%s interprets the next argument in the parameter list as the address (a pointer) of a null-terminated character string (type const char *) which is printed. If the address is 0 (i.e., NULL), the behavior is as if a pointer to the string "NULL" were supplied.

%% causes a single percent sign to be printed. This does not consume an argument from the argument list.

The format argument is the address of the format string, and the format string is terminated by a null character (ascii code 0).

If a NULL pointer is passed as the first parameter, myprintf() should behave as if a pointer to the string "NULL\n" were given as the format string.

Example

extern void myprintf(char *, ...);

int main(void)
{
   myprintf("Simple Test\n");
   myprintf("Simple Test with ignored arguments\n", 1, 2, 3);
   myprintf(NULL);
   myprintf("%s\n", "Hello, World");
   myprintf("%s\n", NULL);
   myprintf("0=%u  4294967295=%u\n", 0, 4294967295UL);
   myprintf("%u%% is perfect\n", 100);
   myprintf("%100xs\n", "Not Used");
   myprintf("%1u %1r %1%\n");
   myprintf("%s", "Go" "od");
   myprintf("%s\n", "bye");

   return 0;
}

Simple Test
Simple Test with ignored arguments
NULL
Hello, World
NULL
0=0  4294967295=4294967295
100% is perfect
%100xs
%1u %1r %1%
Goodbye

Ground Rules

• The only external functions you may use are .udiv.
• The only service requests you may use are "write" and "exit". Only use the "exit" service request if the "write" service request fails. For purposes of this assignment, assume that the "write" service request fails if the "C" bit is set after the trap or the number of characters actually written did not match the number of characters requested to be written. Use the "SYMBOL=value" construct in your program to give appropriate symbolic names to EXIT, WRITE, and STDOUT
• Do not use the %rn names for the registers. Instead, use the %gn, %in, %ln, and %on names. You may not use the %Y register or the floating point registers.
• You are required to implement and use a recursive function which outputs a 32-bit unsigned integer in decimal.
• You are required to implement and use a leaf function which prints a character on the standard output.
• Begin your file with a comment block which includes your name. Precede each function with a block of comments describing the function. The comments will include: how the function is called (what goes in each register), what the function does, the nature of the algorithm, and what (if anything) is returned.
• You must submit a single, plain SPARC assembly language file called myprintf.s which must assemble without warnings or errors using lcc -c -o myprintf.o myprintf.s. The name of the function must be myprintf().
• You may not use a high-level language compiler such as gcc or lcc to generate the assembly code you submit.
• You will lose points if you deviate from the assignment. Use the above list as a final checklist for your program.

Suggestion

Submission

/u/cs217/bin/submit 6 myprintf.s